Nowadays, incandescent light sources are frequently substituted by light emitting arrangements based on solid state light sources. A light emitting arrangement based on a solid state light source, e.g. an LED, has many advantages over an incandescent light source, such as reduced power consumption, long service life, and environmental conservation. However, it is desirable that at least some features of traditional incandescent light sources are adopted by modern light emitting arrangements.
An incandescent light source is a light source that produces light from heat. An incandescent light source changes its color temperature from about 2700 K to about 1900 K, when dimmed from 100% light output to 5% light output. The so-called dimming curve of the light emitted from the incandescent light source ideally follows a planckian curve, also called blackbody curve, in a CIE chromaticity diagram. A lower color temperature makes the light appear more reddish to the human eye. Thus, a lower color temperature is associated with a warmer, cozier and pleasant atmosphere.
It would be desirable to provide a light emitting arrangement, based on a solid state light source, which mimics the behavior of an incandescent light source in the dimmed state, i.e. at low levels of luminous flux. Such behavior is advantageous e.g. when the light emitting arrangement is used in hospitality settings. Preferably, the correlated color temperature of the light emitted from a light emitting arrangement, based on a solid state light source, should also follow a planckian curve in a CIE chromaticity diagram.
WO 2010/103480 disclosed a lighting device comprising an LED driver, a two-terminal LED module, a first LED group and a second LED group, wherein the LED module was designed to vary the LED currents to the first LED group and the second LED group, respectively, such that the color behavior of the light output of the LED module on dimming resembled the color behavior of an incandescent lamp.
However, there is still a need in the art for light emitting arrangements having a relatively low correlated color temperature, similar to the color temperature of an incandescent light source, in the dimmed state, and having a relatively high and constant color rendering index, close to the color rendering index of an incandescent light source.